1. Technical Field
This invention relates generally to thrust washers of the type used to support a rotating shaft, such as a crankshaft, against lateral thrust loads, and more particularly to the construction and method of making such thrust washers.
2. Related Prior Art
Thrust washers are commonly used in many applications where it is necessary to support a rotating crankshaft or the like against lateral thrust loads. In an engine application, for example, the crankshaft is subject to axial thrust loads which act to force the shaft toward displacement along its axis. Traditionally, such thrust washers are made having a bi-metal construction wherein a layer of bearing material such as aluminum-lead or aluminum-tin, is bonded to a supportive backing layer of steel. While such bearings perform satisfactorily, the bi-metal construction adds cost and complexity to the manufacturing of such bearings and makes recycling any scrap material involved in the manufacture of thrust bearing impractical due to the bi-metal combination. Moreover, the steel backing layer is inherently heavier than the aluminum-bearing layer and thus contributes more to the weight of the thrust bearings than does the bearing layer material.
One advantage in manufacturing bi-metal thrust bearings is that they can be manufactured very quickly and inexpensively in a press-forming operation. Blanks or strips of the bi-metal material are stamped and/or coined to shape, including any hydrodynamic features on the thrust face.
In one known application, a thrust bearing has been machined entirely from a block of aluminum alloy material of unknown composition. It is believed that the machine thrust bearing could not be formed using traditional press-forming operations employed in bi-metal type thrust washers. It will be appreciated that the cost and complexity of machining individual thrust washers far outweighs any benefit derived an all-aluminum construction.
A thrust bearing constructed according to the invention overcomes or greatly minimizes the foregoing limitations of the known prior art.
According to the invention, a thrust washer is fabricated entirely of an aluminum alloy material by press-forming.
According to a further aspect of the invention, the aluminum alloy is preferably an aluminum-silicon alloy.
According to a further aspect of the invention, the aluminum-silicon alloy includes at least 2 wt % silicon.
According to a still further aspect of the invention, the silicon content ranges from 2 to 20 wt %.
According to a further aspect of the invention, the aluminum-silicon alloy includes 0.1 to 4 wt % copper.
According to a further aspect of the invention, the aluminum-silicon washer has silicon particles present in the aluminum matrix of a density and size such that there exists at least four silicon particles greater than 5 xcexcm in size when counted in an area 0.04 mm2.
According to yet a further aspect of the invention, the silicon particles are present throughout the matrix and serve to polish the counterface of a crankshaft.
According to a further aspect of the invention, as the thrust face of the washer wears, the aluminum matrix wears and is carried away, but the silicon particles remain embedded at the surface so as to continually increase the density of the silicon particles at the thrust face. Consequently, as the thrust washer wears, its bearing properties actually increase with the accumulation of silicon particles at the thrust surface which enhances the polishing and wear characteristics of the thrust washer.